Managing sub-block erase operations in a memory sub-system

ABSTRACT

A processing device in a memory system connects a first data block of the memory device to a second data block of the memory device to generate a combined data block comprising a first plurality of sub-blocks of the first data block and a second plurality of sub-blocks of the second data block, wherein the connecting includes: for each wordline of a first plurality of wordlines of the first data block, creating a wordline connection short between the respective wordline of the first data block and a corresponding wordline of a second plurality of wordlines of the second data block, wherein the first plurality of wordlines and the second plurality of wordlines comprise data wordlines; and driving a first data wordline of the first data block and a second wordline of the second data block using a single string driver of the memory device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of co-pending U.S.application Ser. No. 17/745,852, filed May 16, 2022, which is acontinuation of U.S. application Ser. No. 16/991,836, filed Aug. 12,2020, which claims the benefit of priority from U.S. ProvisionalApplication No. 62/956,049, filed on Dec. 31, 2019, each of which isincorporated herein by reference.

TECHNICAL FIELD

Embodiments of the disclosure relate generally to memory sub-systems,and more specifically, relate to managing sub-block erase operations ina memory sub-system.

BACKGROUND

A memory sub-system can include one or more memory devices that storedata. The memory devices can be, for example, non-volatile memorydevices and volatile memory devices. In general, a host system canutilize a memory sub-system to store data at the memory devices and toretrieve data from the memory devices.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be understood more fully from the detaileddescription given below and from the accompanying drawings of variousembodiments of the disclosure.

FIG. 1 illustrates an example computing system that includes a memorysub-system in accordance with some embodiments of the presentdisclosure.

FIG. 2 is a block diagram illustrating select gate devices and datastorage device in a data block of a memory device in a memory sub-systemin accordance with some embodiments of the present disclosure.

FIG. 3 is a diagram illustrating the gate voltage step down processusing a string of devices during an erase operation, in accordance withsome embodiments of the present disclosure.

FIG. 4 is a flow diagram of an example method of implementing asub-block erase operations in a memory sub-system, in accordance withsome embodiments of the present disclosure.

FIG. 5 is a flow diagram of an example method of inhibiting theexecution of an erase operation on unselected sub-blocks of a data blockin a memory sub-system, in accordance with some embodiments of thepresent disclosure.

FIG. 6 is a block diagram illustrating shared string drivers betweendata blocks of a memory device in a memory sub-system, in accordancewith some embodiments of the present disclosure.

FIG. 7 illustrates an example machine of a computer system within whicha set of instructions, for causing the machine to perform any one ormore of the methodologies discussed herein, can be executed.

DETAILED DESCRIPTION

Aspects of the present disclosure are directed to managing sub-blockerase operations in a memory sub-system. A memory sub-system can be astorage device, a memory module, or a hybrid of a storage device andmemory module. Examples of storage devices and memory modules aredescribed below in conjunction with FIG. 1 . In general, a host systemcan utilize a memory sub-system that includes one or more components,such as memory devices that store data. The host system can provide datato be stored at the memory sub-system and can request data to beretrieved from the memory sub-system.

A memory device can be a non-volatile memory device. A non-volatilememory device is a package of one or more dies. Each die can consist ofone or more planes. For some types of non-volatile memory devices (e.g.,NAND devices), each plane consists of a set of physical blocks. Eachblock consists of a set of pages. Each page consists of a set of memorycells (“cells”). A cell is an electronic circuit that storesinformation. A data block hereinafter refers to a unit of the memorydevice used to store data and can include a group of memory cells, aword line group, a word line, or individual memory cells. Memory pages(also referred to herein as “pages”) store one or more bits of binarydata corresponding to data received from the host system. The memorycells of a data block can be arranged along a number of separatewordlines. To achieve high density, a string of memory cells in anon-volatile memory device can be constructed to include a number ofmemory cells at least partially surrounding a pillar of channelmaterial. The memory cells can be coupled to access lines, which arecommonly referred to as “wordlines,” often fabricated in common with thememory cells, so as to form an array of strings in a block of memory.The compact nature of certain non-volatile memory devices, such as 3Dflash NAND memory, means wordlines are common to many memory cellswithin a block of memory.

Each data block can include a number of sub-blocks, where each sub-blockis defined by an associated pillar (e.g., a vertical conductive trace)extending from a shared bitline. Each pillar can include a number ofdata storage devices coupled to dummy wordlines (i.e. wordlines that aregenerally not used for storing host data) and data wordlines (i.e.wordlines that are generally used for storing host data).

Sub-blocks of a data block can be accessed separately in certainoperations (e.g., to perform program or read operations), while otheroperations (e.g., block erase operation) apply to the whole data block.Since the data block in certain memory devices (e.g., three-dimensionalNAND) can include a structure to selectively enable the pillarassociated with a certain sub-block, while disabling the pillarsassociated with other sub-blocks, enabling sub-block erase can bedesirable in order to improve the performance and granularity of theblock erase operations of the memory sub-system. In one embodiment, thisstructure for enabling certain pillars while disabling others includesone or more select gate devices positioned at either or both ends ofeach pillar. Depending on a control signal applied, these select gatedevices can either enable or disable the conduction of signals throughthe pillars. In one embodiment, the select gates devices associated witheach pillar in the data block are controlled separately.

Conventional memory devices perform erase operation on the whole datablock with no support for smaller granularity for the size of a memoryregion on which an erase operation is performed. This fixed-size eraseblock introduces latencies for the memory sub-system because eraseoperations are performed at high frequency. Additionally, formulti-dimensional memory devices (e.g., 3D NAND), improved latency isparticularly important in order to take advantage of the advancedarchitecture of the new memory device. In order to enable improvedperformance for the multi-dimensional memory devices, a solution ofperforming erase operations on only certain portions of the data block,thus expediting the erase operations by reducing the number of dataverification operations, may be desired.

Aspects of the present disclosure address the above and otherdeficiencies by enabling the execution of the erase operation onselected sub-blocks of the data block, while inhibiting the execution ofthe erase operation on the unselected sub-blocks of the data block. Inan implementation, all sub-blocks of the data block receive the sameerase signal in the form of an input voltage from the bitline. In orderto inhibit erasing certain sub-blocks, a channel voltage that is appliedat the data wordlines of the excluded sub-block should be as close tozero volts as possible. Reducing the voltage from an input voltage value(e.g., 24 volts) to zero volts can be done gradually in order tominimize disturbances to the memory cells of the excluded sub-block.This can be achieved by gradually reducing the input voltage using agroup of wordlines coupled to a number of select gate devices (SGDs) anda group of wordlines (e.g., dummy wordlines and possibly data wordlines)coupled to a number of data storage devices, such that the gate voltageat each device can be less than the gate voltage at the previous deviceby a predetermined step down interval. The number of SGDs and the groupof wordlines are specific to each sub-block of the data block. Byreducing the gate voltage by a step down interval at each device, whenthe gate voltage arrives at the first data wordline to be used forstoring host data, the value of the pillar voltage received at the firstdata wordline is reduced to approximately 0 volts, thus suppressing theerase operation in the excluded sub-block while minimizing disturbances(e.g., caused by hot electron injection) to the memory cells of theexcluded sub-block.

In certain implementations, two adjacent data blocks can be linked byconnecting adjacent wordlines of the two data blocks using localwordline (WL) connection shorts, such that a WL of one data block isconnected to a corresponding WL of the other data block using theconnection short. When two WLs are connected, a single string driver canbe used for driving the two WLs, thus enabling a single read or programoperation to be applied to the two connected WLs. However, to enableerase operation on a sub-block granularity, it can be desirable to haveseparate string drivers for certain data wordlines. As an example,adding the top-most data wordlines to the group of wordlines wherevoltage step down is applied can ensure that the gate voltage is reducedto at least 0 volts by the time it arrives at the data wordlines thatneeds to be erase suppressed (e.g., data wordlines used for storing hostdata). In this case, the data wordlines of a data block that will beused for voltage step down can have separate string drivers that are notshared by corresponding data wordlines in the other data block. This canbe done by disabling the local connection short for those data wordlinesthat connects the two data blocks, as explained in more details below.

In certain implementations, the memory sub-system can reduce the overallpower consumption of the memory device by reducing the number of voltagesupplies required for supplying voltage to the memory device. Forexample, the memory sub-system can enable sharing of a voltage supplybetween two adjacent devices of the data block by adjusting a thresholdvoltage of each device, such that applying the same voltage at the gateof the adjacent devices can result in the same stepping down voltage ateach device. In implementations, sharing of the voltage supply betweenadjacent devices can be applicable to certain devices including selectgate devices and data storage devices connected to dummy wordlines.

In certain implementations, the memory sub-system can further reduce thedisturbances caused during the voltage step down process (e.g., hotelectron disturbance) by increasing the thickness of the oxide layerbetween certain wordlines of the data block. For example, the thicknessof the oxide layer between the dummy wordlines can be increased by apre-determined amount, thus providing a longer channel for stepping downthe gate voltage before reaching the data wordlines of the data block.In implementations, the predetermined amount of thickness increase inthe oxide can be calculated in order to minimize read performancepenalties of the data block.

The techniques of managing sub-block erase operations of a data block ina memory sub-system that are described herein enable an improved overallperformance of the memory sub-system. Enabling selective sub-blocks forerase operations while inhibiting the erase operation on othersub-blocks increases the granularity of the unit of data where the eraseoperation is to be performed, resulting in more efficient eraseoperations of data blocks in the memory sub-system. For example, theread and write operations that are received at the data block no longerneed to wait for a time-consuming erase operation to be completed beforethey can be executed. Further, because certain sub-blocks can beexcluded from the erase operation, the latency of performing eraseoperations on data blocks of the memory device can be reducesignificantly. Given that erase operations are executed on the memorydevice at a high frequency, reducing the latency or the erase operationwhile increasing the granularity of the erase operation improves theoverall performance of the memory device.

FIG. 1 illustrates an example computing system 100 that includes amemory sub-system 110 in accordance with some embodiments of the presentdisclosure. The memory sub-system 110 can include media, such as one ormore volatile memory devices (e.g., memory device 140), one or morenon-volatile memory devices (e.g., memory device 130), or a combinationof such.

A memory sub-system 110 can be a storage device, a memory module, or ahybrid of a storage device and memory module. Examples of a storagedevice include a solid-state drive (SSD), a flash drive, a universalserial bus (USB) flash drive, an embedded Multi-Media Controller (eMMC)drive, a Universal Flash Storage (UFS) drive, a secure digital (SD)card, and a hard disk drive (HDD). Examples of memory modules include adual in-line memory module (DIMM), a small outline DIMM (SO-DIMM), andvarious types of non-volatile dual in-line memory modules (NVDIMMs).

The computing system 100 can be a computing device such as a desktopcomputer, laptop computer, network server, mobile device, a vehicle(e.g., airplane, drone, train, automobile, or other conveyance),Internet of Things (IoT) enabled device, embedded computer (e.g., oneincluded in a vehicle, industrial equipment, or a networked commercialdevice), or such computing device that includes memory and a processingdevice.

The computing system 100 can include a host system 120 that is coupledto one or more memory sub-systems 110. In some embodiments, the hostsystem 120 is coupled to different types of memory sub-system 110. FIG.1 illustrates one example of a host system 120 coupled to one memorysub-system 110. As used herein, “coupled to” or “coupled with” generallyrefers to a connection between components, which can be an indirectcommunicative connection or direct communicative connection (e.g.,without intervening components), whether wired or wireless, includingconnections such as electrical, optical, magnetic, etc.

The host system 120 can include a processor chipset and a software stackexecuted by the processor chipset. The processor chipset can include oneor more cores, one or more caches, a memory controller (e.g., NVDIMMcontroller), and a storage protocol controller (e.g., PCIe controller,SATA controller). The host system 120 uses the memory sub-system 110,for example, to write data to the memory sub-system 110 and read datafrom the memory sub-system 110.

The host system 120 can be coupled to the memory sub-system 110 via aphysical host interface. Examples of a physical host interface include,but are not limited to, a serial advanced technology attachment (SATA)interface, a peripheral component interconnect express (PCIe) interface,universal serial bus (USB) interface, Fibre Channel, Serial AttachedSCSI (SAS), a double data rate (DDR) memory bus, Small Computer SystemInterface (SCSI), a dual in-line memory module (DIMM) interface (e.g.,DIMM socket interface that supports Double Data Rate (DDR)), etc. Thephysical host interface can be used to transmit data between the hostsystem 120 and the memory sub-system 110. The host system 120 canfurther utilize an NVM Express (NVMe) interface to access the memorycomponents (e.g., memory devices 130) when the memory sub-system 110 iscoupled with the host system 120 by the PCIe interface. The physicalhost interface can provide an interface for passing control, address,data, and other signals between the memory sub-system 110 and the hostsystem 120. FIG. 1 illustrates a memory sub-system 110 as an example. Ingeneral, the host system 120 can access multiple memory sub-systems viaa same communication connection, multiple separate communicationconnections, and/or a combination of communication connections.

The memory devices 130, 140 can include any combination of the differenttypes of non-volatile memory devices and/or volatile memory devices. Thevolatile memory devices (e.g., memory device 140) can be, but are notlimited to, random access memory (RAM), such as dynamic random accessmemory (DRAM) and synchronous dynamic random access memory (SDRAM).

Some examples of non-volatile memory devices (e.g., memory device 130)include negative-and (NAND) type flash memory and write-in-place memory,such as three-dimensional cross-point (“3D cross-point”) memory. Across-point array of non-volatile memory can perform bit storage basedon a change of bulk resistance, in conjunction with a stackablecross-gridded data access array. Additionally, in contrast to manyflash-based memories, cross-point non-volatile memory can perform awrite in-place operation, where a non-volatile memory cell can beprogrammed without the non-volatile memory cell being previously erased.NAND type flash memory includes, for example, two-dimensional NAND (2DNAND) and three-dimensional NAND (3D NAND).

Each of the memory devices 130 can include one or more arrays of memorycells. One type of memory cell, for example, single level cells (SLC)can store one bit per cell. Other types of memory cells, such asmulti-level cells (MLCs), triple level cells (TLCs), and quad-levelcells (QLCs), can store multiple bits per cell. In some embodiments,each of the memory devices 130 can include one or more arrays of memorycells such as SLCs, MLCs, TLCs, QLCs, or any combination of such. Insome embodiments, a particular memory device can include an SLC portion,and an MLC portion, a TLC portion, or a QLC portion of memory cells. Thememory cells of the memory devices 130 can be grouped as pages that canrefer to a logical unit of the memory device used to store data. Withsome types of memory (e.g., NAND), pages can be grouped to form blocks.

Although non-volatile memory components such as a 3D cross-point arrayof non-volatile memory cells and NAND type flash memory (e.g., 2D NAND,3D NAND) are described, the memory device 130 can be based on any othertype of non-volatile memory, such as read-only memory (ROM), phasechange memory (PCM), self-selecting memory, other chalcogenide basedmemories, ferroelectric transistor random-access memory (FeTRAM),ferroelectric random access memory (FeRAM), magneto random access memory(MRAM), Spin Transfer Torque (STT)-MRAM, conductive bridging RAM(CBRAM), resistive random access memory (RRAM), oxide based RRAM(OxRAM), negative-or (NOR) flash memory, electrically erasableprogrammable read-only memory (EEPROM).

A memory sub-system controller 115 (or controller 115 for simplicity)can communicate with the memory devices 130 to perform operations suchas reading data, writing data, or erasing data at the memory devices 130and other such operations. The memory sub-system controller 115 caninclude hardware such as one or more integrated circuits and/or discretecomponents, a buffer memory, or a combination thereof. The hardware caninclude a digital circuitry with dedicated (i.e., hard-coded) logic toperform the operations described herein. The memory sub-systemcontroller 115 can be a microcontroller, special purpose logic circuitry(e.g., a field programmable gate array (FPGA), an application specificintegrated circuit (ASIC), etc.), or other suitable processor.

The memory sub-system controller 115 can include a processor 117 (e.g.,a processing device) configured to execute instructions stored in alocal memory 119. In the illustrated example, the local memory 119 ofthe memory sub-system controller 115 includes an embedded memoryconfigured to store instructions for performing various processes,operations, logic flows, and routines that control operation of thememory sub-system 110, including handling communications between thememory sub-system 110 and the host system 120.

In some embodiments, the local memory 119 can include memory registersstoring memory pointers, fetched data, etc. The local memory 119 canalso include read-only memory (ROM) for storing micro-code. While theexample memory sub-system 110 in FIG. 1 has been illustrated asincluding the memory sub-system controller 115, in another embodiment ofthe present disclosure, a memory sub-system 110 does not include amemory sub-system controller 115, and can instead rely upon externalcontrol (e.g., provided by an external host, or by a processor orcontroller separate from the memory sub-system).

In general, the memory sub-system controller 115 can receive commands oroperations from the host system 120 and can convert the commands oroperations into instructions or appropriate commands to achieve thedesired access to the memory devices 130. The memory sub-systemcontroller 115 can be responsible for other operations such as wearleveling operations, garbage collection operations, error detection anderror-correcting code (ECC) operations, encryption operations, cachingoperations, and address translations between a logical address (e.g.,logical block address (LBA), namespace) and a physical address (e.g.,physical block address) that are associated with the memory devices 130.The memory sub-system controller 115 can further include host interfacecircuitry to communicate with the host system 120 via the physical hostinterface. The host interface circuitry can convert the commandsreceived from the host system into command instructions to access thememory devices 130 as well as convert responses associated with thememory devices 130 into information for the host system 120.

The memory sub-system 110 can also include additional circuitry orcomponents that are not illustrated. In some embodiments, the memorysub-system 110 can include a cache or buffer (e.g., DRAM) and addresscircuitry (e.g., a row decoder and a column decoder) that can receive anaddress from the memory sub-system controller 115 and decode the addressto access the memory devices 130.

In some embodiments, the memory devices 130 include local mediacontrollers 135 that operate in conjunction with memory sub-systemcontroller 115 to execute operations on one or more memory cells of thememory devices 130. An external controller (e.g., memory sub-systemcontroller 115) can externally manage the memory device 130 (e.g.,perform media management operations on the memory device 130). In someembodiments, a memory device 130 is a managed memory device, which is araw memory device combined with a local controller (e.g., localcontroller 135) for media management within the same memory devicepackage. An example of a managed memory device is a managed NAND (MNAND)device.

In one embodiment, the memory sub-system 110 includes sub-block erasemanagement component 113 that can be used to perform an erase operationon one or more sub-blocks of a data block of memory device 130 or memorydevice 140, while preventing other sub-blocks of the data block frombeing erased by the erase operation. In implementations, in order toinhibit erasing the unselected sub-blocks of the data block, a gatevoltage that is applied at the data wordlines of the unselectedsub-blocks can be reduced to approximately zero volts, thus suppressingthe erase signal applied at the unselected sub-blocks and preventing thedata stored at the data wordlines from being erased. Sub-block erasemanagement component 113 can reduce the gate voltage from an inputvoltage value (e.g., 24 volts) to zero volts gradually in order tominimize disturbances to the memory cells of the unselected sub-block.Sub-block erase management component 113 can reduce the gate voltageusing a group of wordlines coupled to a number of select gate devices(SGDs) and a group of wordlines (e.g., dummy wordlines) coupled to anumber of data storage devices, such that the gate voltage at eachwordline can be less than the gate voltage at the previous wordline by apredetermined step down interval (e.g., a step down interval of 3.5V).

In one implementation, sub-block erase management component 113 canfurther enable the top most one or more data wordlines (i.e., the one ormore data wordlines closest to the shared bitline) of the unselectedsub-block to be driven by a separate string driver than correspondingtop most data wordlines of an adjacent sub-block of the data block. Asan illustrative example, two adjacent data blocks can be linked byconnecting adjacent data wordlines of the two data blocks using localwordline (WL) connection shorts, such that a data wordline of one datablock is connected to a corresponding data wordline of the other datablock using the connection short. When the two data wordlines areconnected, a single string driver can be used for driving the two datawordlines, thus enabling a single read or program operation to beapplied to the two connected wordlines. However, to enable eraseoperation on a single sub-block, one or more data wordlines of theunselected sub-blocks can require separate string drivers than the datawordlines of the selected sub-block (e.g., because one or more datawordlines of the unselected sub-block can be used in voltage step downprocess). In this case, sub-block erase management component 113 candisable the local connection short for the data wordlines that will beused in the voltage step down process, as explained in more details inFIG. 2 . Consequently, different gate voltage can be applied to the datawordlines that are used for voltage step down than the gate voltageapplied to data wordlines that included in the erase operation.

In certain implementations, sub-block erase management component 113 canimprove the power consumption of memory device 130 by reducing thenumber of voltage supplies required for supplying voltage to memorydevice 130. In this case, sub-block erase management component 113 canenable sharing of a voltage supply between two adjacent devices of thedata block by adjusting a threshold voltage of each device, such thatapplying the same voltage at the gate of the adjacent devices can resultin the same stepping down voltage at each device. In implementations,sharing of the voltage supply between adjacent devices can be applicableto certain devices including select gate devices and data storagedevices connected to dummy wordlines.

In certain implementations, sub-block erase management component 113 canfurther reduce disturbance to the memory cells of the data block thatcan be caused by hot electron injection that can be generated as aresult of the voltage step down process. For example, when the gatevoltage is abruptly reduced at a given wordline, the wordline can sufferfrom hot-electron (“hot-e”) disturb where a large voltage differentialbetween the gate and source causes the residue electrons to be injectedfrom a drain depletion region into the floating gate. In this case,sub-block erase management component 113 can enable increasing thethickness of the oxide layer between certain wordlines of the data blockto increase an internal channel length to provide better signalisolation. For example, the thickness of the oxide layer between thedummy wordlines can be increased by a pre-determined amount, thusproviding a longer channel for stepping down the gate voltage beforereaching the data wordlines of the data block. In implementations, thepredetermined amount of thickness increase in the oxide can becalculated in order to minimize read performance penalties of the datablock.

FIG. 2 is a block diagram illustrating select gate devices and datastorage devices in a data block of a memory device in a memorysub-system in accordance with some embodiments of the presentdisclosure. In one embodiment, data block 200 is representative of anyof the data blocks that make up memory device 130 or memory device 140.Data block 200 can be one of a number of physical blocks in the memorydevice and can include a set of memory pages. The memory pages store oneor more bits of binary data corresponding to data received from the hostsystem. The memory cells of data block 200 can be arranged along anumber of separate wordlines 230 and 233. Data block 200 can include ashared bitline 210 having a number of pillars 212, 214, 216, 218extending therefrom to a separate source line 220. Each pillar can be avertical conductive trace and the intersections of each of pillars 212,214, 216, 218 and of each of wordlines 230 and 233 form the memorycells. Thus, each of pillars 212, 214, 216, 218 forms a separatesub-block within data block 200, where each sub-block can be accessseparately. To enable an access operation, such as a program operationor a read operation, to be performed on a given sub-block, data block200 includes a number of select gate devices to selectively enable thepillar (e.g., pillar 212) associated with a certain sub-block, whiledisabling the pillars (e.g., pillars 214, 216, 218) associated withother sub-blocks. For example, each pillar can include a number ofselect gate devices (e.g., SGD0, SGD1, SGD2) at a first end (e.g., adrain end) and a number of select gate devices (e.g., SGS0, SGS1, SGS2)at a second end (e.g., a source end). In other examples, a differentnumber of select gate devices can be used at each end of the sub-block.

In one embodiment, the select gate devices in data block 200 are formedusing programmable replacement gate transistors. Thus, the select gatedevices have a programmed threshold voltage. Depending on a magnitude ofa control signal applied relative to the threshold voltage, the selectgate devices can either enable or disable the conduction of signalsthrough the corresponding pillar. For example, if the magnitude of thecontrol signal applied to a select gate device is less than thethreshold voltage, the select gate device can be turned off and canprevent signal flow through the corresponding pillar. Conversely, if themagnitude of the control signal is greater than the threshold voltage,the select gate device can be turned on and can permit signal flowthrough the corresponding pillar. In one embodiment, the select gatesdevices associated with each pillar in data block 200 are controlledseparately, such that signal flow can be prevented in certain pillarswhile permitted in other pillars at the same time. Replacement gatetransistors have a relatively short internal channel length, and thusare susceptible to some amount of signal leakage. Accordingly, in oneembodiment, each pillar in data block 200 has multiple select gatedevices at each of the drain end and the source end, effectivelyincreasing the internal channel length to provide better signalisolation when turned off.

Following the select gate devices on the vertical conductive trace aredata storage devices that are coupled to dummy wordlines 230 thenanother group of data storage devices that are coupled to data wordlines233. In certain implementations, in order to support improved latencyfor multi-dimensional memory devices (e.g., 3D NAND), memory sub-system110 can enable connecting two adjacent data blocks to form data block200. As an example, memory sub-system 110 can connect sub-block 214 ofone data block to sub-block 216 of an adjacent data block using localwordline (WL) connection shorts 235 between data wordlines 233, suchthat a data WL of sub-block 214 is connected to a corresponding data WLof sub-block 216 using the connection short. These connection shorts,however, result in the same voltage being applied to the data wordlinesthat are connected together. Given that excluding certain sub-blocksfrom an erase operation can require different voltage to be applied tothe top most data wordlines of the excluded sub-block than the voltageapplied at the top-most data wordlines for the sub-block included in theerase, the connection short can be eliminated for certain datawordlines. For example, the top most data wordline 234 can have aseparate string driver in order to enable a different voltage to beapplied to data wordline 234, without affecting a corresponding datawordline in an adjacent sub-block. Therefore, as shown in FIG. 2 , datawordline 234 of sub-block 212 can be disconnected from the correspondingdata wordline of sub-block 214. Accordingly, because there is noconnection short for the top-most data wordline 234 of data block 200,data wordline 234 can be used in the process of stepping the gatevoltage to exclude sub-block 212 from an erase operation, while thecorresponding data wordline of sub-block 214 can have a differentvoltage applied to it to include sub-block 214 in the erase operation.

FIG. 3 is a diagram illustrating the gate voltage step down processusing a string of devices during an erase operation, in accordance withsome embodiments of the present disclosure. In one embodiment, string320 can be the same or similar to pillar 212 illustrated in FIG. 2 . Asdescribed above, string 320 includes a number of drain select gate (KM)devices SGD0-SGD4, a number of data storage devices, each connected to aseparate wordline (WL) WLn-WLn+3, In one embodiment, one or more of thedata storage devices are connected to a dummy word line WLn+1 to WLn+3and are generally not used for storing data. String 320 can furtherinclude a number of data storage devices connected to data WLs. At leastone data WL WLn can be used in the voltage step sown process. Dependingon the embodiment, there can be any number of data word lines. In oneembodiment, string 320 represents a sub-block of a data block that isexcluded from the erase operation. As described above, the data blockcan include additional sub-blocks having additional strings of devices.

As described above with respect to FIG. 1 , in one embodiment, sub-blockerase management component 113 can apply different voltage signals tothe gate terminal of the different devices of string 320 to graduallydecrease an input voltage during an erase operation, such that the datawordlines of string 320 are excluded from the erase operation. Thisvoltage can be referred to as the gate voltage (Vg). Additionally, eachof the devices in string 320 has an associated threshold voltage (Vt)which represents a voltage at which each device switches from an “off”state to an “on” state, or vice versa. As an example, each of the SGDdevices SGD0-SGD4 and the data storage devices WLn-WLn+3 can have athreshold voltage of 3V. In one implementation, the channel potential310 of string 320 represents a difference between a voltage applied atthe control gate of each device (i.e., a gate voltage (Vg)) and athreshold voltage of the device (Vt).

In certain implementations, sub-block erase management component 113 candetermine a step down interval to use for gradually reducing the gatevoltage at each successive device, such that the gate voltage that isapplied to the first data wordline that will be used for storing hostdata can reach a threshold level. In an implementation, the thresholdlevel can be an amount of voltage that is small enough such that thedata stored at the data wordlines are preserved and not erased. Forexample, the threshold level can be approximately zero volts. In certainimplementations, memory sub-system 110 can use a step down interval ofapproximately 3.5 volts when reducing the gate voltage that is appliedat each wordline that is connected to each SGD, each dummy wordline, andeach data wordline that is used in the stepping down process of the gatevoltage, such that the voltage applied at each wordline is less than thevoltage applied at the previous wordline by approximately 3.5 volts. Forexample, if the gate voltage step down process start at SGD2 with a Vgat SGD2=23.5V, then Vg at SGD1 can be 20V (i.e., a gate voltage of 23.5Vat the previous SGD2 minus the step down interval of 3.5V). By reducingVg at each device SGD0-SGD4 and WLn-WLn+3 by the 3.5V step downinterval, the result can be a Vg of 13V at WLn+3, a Vg of 9.5V at WLn+2,a Vg of 6V at WLn+1, and a Vg of 2.5V at WLn.

Gradually stepping down the gate voltage is desirable to avoid a sharpchange in channel potential between WLn+3 and WLn. Such a sharp changein channel potential can create a large electric field, leading toincreased hot electron injection, which would magnify erase disturbproblems for the data wordlines of string 320. As illustrated in FIG. 3, by gradually decreasing the gate voltage at each device, channelpotential 310 is also decreased gradually, thus minimizing disturbancesto the data wordlines. As a result, channel potential 320 on thedrain-side of SGD2 is 20.5V (i.e., a gate voltage of 23.5V minus athreshold voltage of 3V). Similarly, channel potential 320 at SGD1 is17V (20V-3V), channel potential 320 at SGD0 is 13.5V. Channel potential320 continues to decrease gradually at dummy wordlines WLn+3-WLn+1 anddata wordline WLn, such that channel potential 320 at WLn+3 is 10V,channel potential 320 at WLn+2 is 6.5V, and channel potential 320 atWLn+1 is 3V. The channel potential 320 is around −0.5V when it arrivesat the first data wordline WLn. Because channel potential 320 is closeto zero at the data wordlines used for storing data, the erase signalwill not affect the data stored at the data wordlines of string 320,thus the data will be excluded from erase.

FIG. 4 is a flow diagram of an example method of implementing asub-block erase operations in a memory sub-system, in accordance withsome embodiments of the present disclosure. The method 400 can beperformed by processing logic that can include hardware (e.g.,processing device, circuitry, dedicated logic, programmable logic,microcode, hardware of a device, integrated circuit, etc.), software(e.g., instructions run or executed on a processing device), or acombination thereof. In some embodiments, the method 400 is performed bysub-block erase management component 113 of FIG. 1 . Although shown in aparticular sequence or order, unless otherwise specified, the order ofthe processes can be modified. Thus, the illustrated embodiments shouldbe understood only as examples, and the illustrated processes can beperformed in a different order, and some processes can be performed inparallel. Additionally, one or more processes can be omitted in variousembodiments. Thus, not all processes are required in every embodiment.Other process flows are possible.

At operation 410, the processing logic receives an erase request toerase data stored at a data block of memory device 130. Inimplementations, the erase request identifies a selected sub-block of aset of sub-blocks of the data block for erase. In one implementations,each sub-block of the data block can include a number of select gatedevices (SGDs) and a number of data storage devices, as explained inmore details herein above.

At operation 420, the processing device loops through the set ofsub-blocks not selected for erase to gradually suppress an input voltagesignal, such that the data stored at data wordlines of the unselectedsub-blocks is not erased. As explained above, the processing logicapplies an input voltage (e.g., 24V) at a bitline of each sub-block ofthe data block.

At operation 430, for each unselected sub-block, the processing logicapplies different gate voltages to the wordlines coupled to the SDGdevices of the sub-block and to a group of wordlines associated withdata storage devices, such that each voltage applied to a successivewordline is less than a previous voltage applied to a previous wordlineby an amount equal to a step down interval (e.g., 3.5V interval). Inimplementations, the voltage stepping down process further include thateach wordline has a threshold voltage that is lower than the gatevoltage at the device (e.g., a threshold voltage of 3V), as explained inmore details here. In this case, when the voltage stepping down processis complete, the gate voltage is reduced to at least 0 volts at thefirst usable data wordline of the sub-block (e.g., data wordlines usedfor storing host data).

At operation 440, the processing logic performs an erase operation toerase data stored at the selected sub-block, while inhibiting the erasefor data stored at the unselected sub-blocks, as explained in moredetails herein above.

FIG. 5 is a flow diagram of an example method of inhibiting theexecution of an erase operation on unselected sub-blocks of a data blockin a memory sub-system, in accordance with some embodiments of thepresent disclosure. The method 500 can be performed by processing logicthat can include hardware (e.g., processing device, circuitry, dedicatedlogic, programmable logic, microcode, hardware of a device, integratedcircuit, etc.), software (e.g., instructions run or executed on aprocessing device), or a combination thereof. In some embodiments, themethod 500 is performed by sub-block erase management component 113 ofFIG. 1 . Although shown in a particular sequence or order, unlessotherwise specified, the order of the processes can be modified. Thus,the illustrated embodiments should be understood only as examples, andthe illustrated processes can be performed in a different order, andsome processes can be performed in parallel. Additionally, one or moreprocesses can be omitted in various embodiments. Thus, not all processesare required in every embodiment. Other process flows are possible.

At operation 510, the processing logic receives a request to erase datastored at a data block of memory device 130. In certain implementations,the data block include a set of sub-blocks and the request identifiesone or more selected sub-blocks of the set of sub-blocks of the datablock to be erased. The other sub-blocks not identified in the eraserequest are excluded from erasing. In one implementations, eachsub-block of the data block can include a number of select gate devices(SGDs) and a number of data storage devices, as explained in moredetails herein above.

At operation 520, the processing device loops through the set ofsub-blocks of the data block to identify whether or not the sub-blockcan be erased. At operation 525, if the processing logic determines thata sub-block is selected for erasing, the processing logic can continuethe loop to the next sub-block because the selected sub-block can beready for the erase operation to be performed.

On the other hand, if the processing logic determines that the sub-blockis unselected for erase, the processing logic at operation 530 can starta voltage step down process using a group of wordlines coupled to SGDdevices, a group of dummy wordlines, and one or more data wordlines, asexplained in more details herein above. As explained above, after thevoltage step down process is completed, a gate voltage applied at datawordlines storing host data can be approximately zero volts, thusprohibiting the data stored at the wordlines form being erased, asexplained in more details herein above.

At operation 535, if the processing logic completes looping through thesub-blocks of the data block, the processing logic, at operation 540,can perform an erase operation to erase data stored at selectedsub-blocks of the data blocks. In this case, because the gate voltagehas been reduced to zero volts at the data wordlines of the unselectedsub-blocks, whereas the gate voltage at the data wordlines of theselected sub-blocks remains high (e.g., 24V), the erase operation willonly erase data stored at the selected sub-blocks. On the other hand, ifthe processing logic at operation 535 determines that more sub-blocksneed to be checked, the processing logic can loop back to operation 520to evaluate the next sub-block of the data block.

FIG. 6 is a block diagram illustrating shared string drivers betweendata blocks of a memory device in a memory sub-system, in accordancewith some embodiments of the present disclosure. In implementations, theability to support sub-block erase in a memory sub-system facilitatesthe feature of shared string drivers between data blocks, which resultsin increased size of the data block. Given that sub-block erase enablesan erase operation to be performed on one or more sub-blocks of the datablock, the increased size of the data block, due to the sharing thestring drivers between adjacent blocks, can have minimal effect on theperformance of the erase operations of the memory devices.

Data block 620 and data block 630 are two adjacent data blocks thatshare string driver 622 and string driver 624, in order to reducelatency of read and write operation of data blocks 620, 630. In certainimplementations, string driver 622 and string driver 624 can bepositioned equally across the wordlines of each data block, such thatthe latency of each wordline is reduces to one fourth of the latencyvalue in the conventional approach where each data block is driven by asingle string driver that is placed at one end of the data block. In anillustrative example, the wordline latency can be measured by a constantcalled a resistance-capacitance (RC) time constant of the wordline, suchthat a lower resistance in the wordline can lead to a lower value of theRC time constant, and a faster performing memory device. The wordline RCtime constant is highly affected by the length of the wordline because along wordline can lead to a higher RC than a shorter wordline.Therefore, by utilizing string driver 622 and string driver 624 withindata block 620, a wordline of data block 620 can be divided into fourportion with string driver 622 driving two portion in two directions andstring driver 624 driving the other two portions in the same twodirections, as shown by the dotted arrows in FIG. 6 . Accordingly, thewordline RC constant is reduced by one fourth of the wordline RCconstant when only one string driver is used for driving each datablock.

FIG. 7 illustrates an example machine of a computer system 700 withinwhich a set of instructions, for causing the machine to perform any oneor more of the methodologies discussed herein, can be executed. In someembodiments, the computer system 700 can correspond to a host system(e.g., the host system 120 of FIG. 1 ) that includes, is coupled to, orutilizes a memory sub-system (e.g., the memory sub-system 110 of FIG. 1) or can be used to perform the operations of a controller (e.g., toexecute an operating system to perform operations corresponding to thesub-block erase management component 113 of FIG. 1 ). In alternativeembodiments, the machine can be connected (e.g., networked) to othermachines in a LAN, an intranet, an extranet, and/or the Internet. Themachine can operate in the capacity of a server or a client machine inclient-server network environment, as a peer machine in a peer-to-peer(or distributed) network environment, or as a server or a client machinein a cloud computing infrastructure or environment.

The machine can be a personal computer (PC), a tablet PC, a set-top box(STB), a Personal Digital Assistant (PDA), a cellular telephone, a webappliance, a server, a network router, a switch or bridge, or anymachine capable of executing a set of instructions (sequential orotherwise) that specify actions to be taken by that machine. Further,while a single machine is illustrated, the term “machine” shall also betaken to include any collection of machines that individually or jointlyexecute a set (or multiple sets) of instructions to perform any one ormore of the methodologies discussed herein.

The example computer system 700 includes a processing device 702, a mainmemory 704 (e.g., read-only memory (ROM), flash memory, dynamic randomaccess memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM(RDRAM), etc.), a static memory 706 (e.g., flash memory, static randomaccess memory (SRAM), etc.), and a data storage system 718, whichcommunicate with each other via a bus 730.

Processing device 702 represents one or more general-purpose processingdevices such as a microprocessor, a central processing unit, or thelike. More particularly, the processing device can be a complexinstruction set computing (CISC) microprocessor, reduced instruction setcomputing (RISC) microprocessor, very long instruction word (VLIW)microprocessor, or a processor implementing other instruction sets, orprocessors implementing a combination of instruction sets. Processingdevice 702 can also be one or more special-purpose processing devicessuch as an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA), a digital signal processor (DSP),network processor, or the like. The processing device 702 is configuredto execute instructions 726 for performing the operations and stepsdiscussed herein. The computer system 700 can further include a networkinterface device 708 to communicate over the network 720.

The data storage system 718 can include a machine-readable storagemedium 724 (also known as a computer-readable medium) on which is storedone or more sets of instructions 726 or software embodying any one ormore of the methodologies or functions described herein. Theinstructions 726 can also reside, completely or at least partially,within the main memory 704 and/or within the processing device 702during execution thereof by the computer system 700, the main memory 704and the processing device 702 also constituting machine-readable storagemedia. The machine-readable storage medium 724, data storage system 718,and/or main memory 704 can correspond to the memory sub-system 110 ofFIG. 1 .

In one embodiment, the instructions 726 include instructions toimplement functionality corresponding to the sub-block erase managementcomponent 113 of FIG. 1 ). While the machine-readable storage medium 724is shown in an example embodiment to be a single medium, the term“machine-readable storage medium” should be taken to include a singlemedium or multiple media that store the one or more sets ofinstructions. The term “machine-readable storage medium” shall also betaken to include any medium that is capable of storing or encoding a setof instructions for execution by the machine and that cause the machineto perform any one or more of the methodologies of the presentdisclosure. The term “machine-readable storage medium” shall accordinglybe taken to include, but not be limited to, solid-state memories,optical media, and magnetic media.

Some portions of the preceding detailed descriptions have been presentedin terms of algorithms and symbolic representations of operations ondata bits within a computer memory. These algorithmic descriptions andrepresentations are the ways used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of operations leading to adesired result. The operations are those requiring physicalmanipulations of physical quantities. Usually, though not necessarily,these quantities take the form of electrical or magnetic signals capableof being stored, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. The presentdisclosure can refer to the action and processes of a computer system,or similar electronic computing device, that manipulates and transformsdata represented as physical (electronic) quantities within the computersystem's registers and memories into other data similarly represented asphysical quantities within the computer system memories or registers orother such information storage systems.

The present disclosure also relates to an apparatus for performing theoperations herein. This apparatus can be specially constructed for theintended purposes, or it can include a general purpose computerselectively activated or reconfigured by a computer program stored inthe computer. Such a computer program can be stored in a computerreadable storage medium, such as, but not limited to, any type of diskincluding floppy disks, optical disks, CD-ROMs, and magnetic-opticaldisks, read-only memories (ROMs), random access memories (RAMs), EPROMs,EEPROMs, magnetic or optical cards, or any type of media suitable forstoring electronic instructions, each coupled to a computer system bus.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general purposesystems can be used with programs in accordance with the teachingsherein, or it can prove convenient to construct a more specializedapparatus to perform the method. The structure for a variety of thesesystems will appear as set forth in the description below. In addition,the present disclosure is not described with reference to any particularprogramming language. It will be appreciated that a variety ofprogramming languages can be used to implement the teachings of thedisclosure as described herein.

The present disclosure can be provided as a computer program product, orsoftware, that can include a machine-readable medium having storedthereon instructions, which can be used to program a computer system (orother electronic devices) to perform a process according to the presentdisclosure. A machine-readable medium includes any mechanism for storinginformation in a form readable by a machine (e.g., a computer). In someembodiments, a machine-readable (e.g., computer-readable) mediumincludes a machine (e.g., a computer) readable storage medium such as aread only memory (“ROM”), random access memory (“RAM”), magnetic diskstorage media, optical storage media, flash memory components, etc.

In the foregoing specification, embodiments of the disclosure have beendescribed with reference to specific example embodiments thereof. Itwill be evident that various modifications can be made thereto withoutdeparting from the broader spirit and scope of embodiments of thedisclosure as set forth in the following claims. The specification anddrawings are, accordingly, to be regarded in an illustrative senserather than a restrictive sense.

What is claimed is:
 1. A system comprising: a memory device; and aprocessing device, operatively coupled with the memory device, toperform operations comprising: connecting a first data block of thememory device to a second data block of the memory device to generate acombined data block comprising a first plurality of sub-blocks of thefirst data block and a second plurality of sub-blocks of the second datablock, wherein the connecting comprises: for each wordline of a firstplurality of wordlines of the first data block, creating a wordlineconnection short between the respective wordline of the first data blockand a corresponding wordline of a second plurality of wordlines of thesecond data block, wherein the first plurality of wordlines and thesecond plurality of wordlines comprise data wordlines; and driving afirst data wordline of the first data block and a second wordline of thesecond data block using a single string driver of the memory device. 2.The system of claim 1, wherein the operations further comprises:receiving an erase request to erase a sub-block of a plurality ofsub-blocks of the first data block, the erase request identifying aselected sub-block of the plurality of sub-blocks of the first datablock for erase, each of the plurality of sub-blocks comprising one ormore select gate devices (SGDs) and a plurality of data storage devices;and for each sub-block of the plurality of sub-blocks not selected forerase: applying an input voltage at a bitline of the first data block;and applying a plurality of gate voltages to a plurality of wordlines ofthe respective sub-block, the plurality of wordlines comprising one ormore wordlines coupled to the one or more SGDs and one or more dummywordlines coupled to a first subset of the plurality of data storagedevices, wherein a voltage of the plurality of gate voltages applied toa successive wordline of the plurality of wordlines is less than aprevious voltage applied to a previous wordline.
 3. The system of claim2, wherein the voltage of the plurality of gate voltages applied to thesuccessive wordline of the plurality of wordlines is less than theprevious voltage applied to the previous wordline by an amount equal toa step down interval.
 4. The system of claim 3, wherein the inputvoltage equals approximately 24 volts, and wherein the step downinterval equals approximately 4 volts.
 5. The system of claim 2, whereinthe input voltage is reduced to a threshold level at a first datawordline that is used for storing host data.
 6. The system of claim 2,wherein each device of the one or more SGDs and the plurality of datastorage devices has an associated threshold voltage that is lower thanthe input voltage.
 7. The system of claim 6, wherein the thresholdvoltage equals approximately 3 volts.
 8. The system of claim 2, whereinthe operations further comprises: connecting a voltage supply to twoadjacent SGDs of the one or more SGDs to enable sharing of the voltagesupply between the two adjacent SGDs.
 9. The system of claim 2, whereinthe operations further comprises: connecting a voltage supply to twoadjacent dummy wordlines of the one or more dummy wordlines to enablesharing of the voltage supply between the two adjacent dummy wordlines.10. The system of claim 2, wherein a first thickness of a first oxidelayer disposed between two adjacent dummy wordlines of the one or moreof dummy wordlines is greater than a second thickness of a second oxidelayer disposed between two adjacent data wordlines of one or more datawordlines of the first data block.
 11. A method comprising: connecting,by a processing device, a first data block of a memory device to asecond data block of the memory device to generate a combined data blockcomprising a first plurality of sub-blocks of the first data block and asecond plurality of sub-blocks of the second data block, wherein theconnecting comprises: for each wordline of a first plurality ofwordlines of the first data block, creating a wordline connection shortbetween the respective wordline of the first data block and acorresponding wordline of a second plurality of wordlines of the seconddata block, wherein the first plurality of wordlines and the secondplurality of wordlines comprise data wordlines; and driving a first datawordline of the first data block and a second wordline of the seconddata block using a single string driver of the memory device.
 12. Themethod of claim 11, further comprising: receiving an erase request toerase a sub-block of a plurality of sub-blocks of the first data block,the erase request identifying a selected sub-block of the plurality ofsub-blocks of the first data block for erase, each of the plurality ofsub-blocks comprising one or more select gate devices (SGDs) and aplurality of data storage devices; and for each sub-block of theplurality of sub-blocks not selected for erase: applying an inputvoltage at a bitline of the first data block; and applying a pluralityof gate voltages to a plurality of wordlines of the respectivesub-block, the plurality of wordlines comprising one or more wordlinescoupled to the one or more SGDs and one or more dummy wordlines coupledto a first subset of the plurality of data storage devices, wherein avoltage of the plurality of gate voltages applied to a successivewordline of the plurality of wordlines is less than a previous voltageapplied to a previous wordline.
 13. The method of claim 12, wherein thevoltage of the plurality of gate voltages applied to the successivewordline of the plurality of wordlines is less than the previous voltageapplied to the previous wordline by an amount equal to a step downinterval.
 14. The method of claim 12, wherein the input voltage isreduced to a threshold level at a first data wordline that is used forstoring host data.
 15. The method of claim 12, wherein each device ofthe one or more SGDs and the plurality of data storage devices has anassociated threshold voltage that is lower than the input voltage. 16.The method of claim 12, further comprising: connecting a voltage supplyto two adjacent SGDs of the one or more SGDs to enable sharing of thevoltage supply between the two adjacent SGDs.
 17. The method of claim12, further comprising: connecting a voltage supply to two adjacentdummy wordlines of the one or more dummy wordlines to enable sharing ofthe voltage supply between the two adjacent dummy wordlines.
 18. Themethod of claim 12, wherein a first thickness of a first oxide layerdisposed between two adjacent dummy wordlines of the one or more ofdummy wordlines is greater than a second thickness of a second oxidelayer disposed between two adjacent data wordlines of one or more datawordlines of the first data block.
 19. A non-transitorycomputer-readable storage medium comprising instructions that, whenexecuted by a processing device, cause the processing device to performoperations comprising: connecting a first data block of a memory deviceto a second data block of the memory device to generate a combined datablock comprising a first plurality of sub-blocks of the first data blockand a second plurality of sub-blocks of the second data block, whereinthe connecting comprises: for each wordline of a first plurality ofwordlines of the first data block, creating a wordline connection shortbetween the respective wordline of the first data block and acorresponding wordline of a second plurality of wordlines of the seconddata block, wherein the first plurality of wordlines and the secondplurality of wordlines comprise data wordlines; and driving a first datawordline of the first data block and a second wordline of the seconddata block using a single string driver of the memory device.
 20. Thenon-transitory computer-readable storage medium of claim 19, wherein theoperations further comprises: receiving an erase request to erase asub-block of a plurality of sub-blocks of the first data block, theerase request identifying a selected sub-block of the plurality ofsub-blocks of the first data block for erase, each of the plurality ofsub-blocks comprising one or more select gate devices (SGDs) and aplurality of data storage devices; and for each sub-block of theplurality of sub-blocks not selected for erase: applying an inputvoltage at a bitline of the first data block; and applying a pluralityof gate voltages to a plurality of wordlines of the respectivesub-block, the plurality of wordlines comprising one or more wordlinescoupled to the one or more SGDs and one or more dummy wordlines coupledto a first subset of the plurality of data storage devices, wherein avoltage of the plurality of gate voltages applied to a successivewordline of the plurality of wordlines is less than a previous voltageapplied to a previous wordline.